As is known, a reverse osmosis (RO) water filtering process uses a semi-permeable membrane that has the ability to remove and reject a wide spectrum of impurities and contaminants from water using only water pressure. These contaminants are automatically rinsed down the drain. The purified water is then stored in a tank for dispensing through an auxiliary faucet.
A typical residential RO water filtering system is installed under a kitchen sink and includes a filter assembly, a reverse osmosis membrane, a storage tank, and an auxiliary faucet attached to the sink. The filter assembly includes a sediment filter and a carbon filter. Intake water enters the system from a cold-water source and is routed through the filter system. The sediment filter removes sediment such as sand and dirt and the like from the intake water, while the carbon filter removes chlorine and other contaminants that cause bad color, odor and taste. The filtered water is then routed to the RO membrane.
The RO membrane includes three ports: an intake port, a permeate outlet port, and a concentrate outlet port. The intake port receives filtered intake water from the filter assembly, and permeate passes through the membrane to the permeate outlet port, while the concentrate water does not pass through the membrane but is directed to the concentrate outlet port. Concentrate water is routed from the concentrate outlet port through a flow restrictor for disposal down a drain of the sink.
Most plumbing codes specify that an anti-siphon or air gap must be located between the concentrate outlet port and the drain. This prevents development of a vacuum in the system that could cause drain or wastewater to be siphoned back into the RO system and contaminate the water supply connected to the RO system. The auxiliary faucet, normally also includes an air gap connecting the concentrate outlet port and the drain.
The permeate is routed from the permeate outlet port to the tank to be stored under pressure. An automatic shut-off valve stops the flow of water to the membrane and to the tank when the tank is full. When the auxiliary faucet is opened by a user, permeate is forced from the tank, through a carbon filter, and out the faucet.
In a typical RO system, especially in the type of RO system used in homes, the rate at which treated water or “permeate” is produced by the system can be very low. As a result, the storage tank is used to store permeate, so that relatively large quantities can be made available when the consumer opens the tap or faucet. In the past, “pre-charged” storage tanks were used. In this type of storage tank, a bladder is used to define a pressurized chamber, usually filled with a compressible gas, such as nitrogen. The bladder isolates the gas from the permeate received by the tank. As the permeate is received by the tank, the permeate gradually compresses the gas in the pressurized chamber. As a result, the permeate is stored under pressure, such that when the tank is opened, the pressure in the storage tank exerted by the compressed gas, forces permeate out of the tank to the faucet.
Although these storage tanks are widely used and provide a suitable means for storing permeate, the storage tanks do have a significant drawback. As more and more permeate is received by the tank, the pressure needed to effect flow of permeate into the tank increases because as the gas chamber is compressed, forces on the bladder increase and the backpressure in the system increases. Accordingly, in order to completely fill the storage tank, a significant pressure must be applied to the permeate as the capacity of the tank is reached. This pressure increase reduces the efficiency of the RO membrane.
This resistance to flow exerted by the storage tank decreases the production rate of the RO system, since the RO system relies on differential pressures between the source and the output to effect flow across the membrane. In addition, as permeate is discharged by the storage tank, the permeate delivery pressure is gradually reduced as the pressurized gas chamber expands. This reduced delivery pressure is observable at the auxiliary faucet. Further examples of prior art systems are shown in U.S. Pat. Nos. 6,764,595; 6,110,360; 5,132,017; 4,853,117; and 4,705,625, each of which is incorporated herein by reference in its entirety.
What is still desired is a new and improved RO water filtering system. Preferably, the RO water filtering system will include an improved permeate storage arrangement that reduces backpressure within the system and/or provides a steadier pressure at the faucet.